At present, components and parts in conventional motor vehicle passive safety systems are used to mainly protect passengers in front seats. Besides safety belts, these components and parts include front airbags and side airbags. Generally, the front airbags and side airbags are inflated by gas generators to protect passengers. The as generators are ignited under the control of main control units, which presents good results and saves thousands of lives. Moreover, for protecting passengers in rear seats, most motor vehicles are equipped only with safety belts. However, safety belts can restrain the rear passengers' bodies, but they cannot protect the rear passengers' head and neck, so the rear passengers' head and neck are often injured by excessive stretching.
According to CNCAP Crash Test 2012 edition, that is, new car assessment program on rear passenger injuries 2012 edition, in a total of eighteen kinds of tested vehicles, only two kinds of vehicles get full marks for protecting rear passengers' heads and necks in frontal impact test against rigid barrier, with 100% overlapping at 50 km/h and frontal impact test against deformable barrier with 40% overlapping at 64 km/h. Even some CNCAP five-star vehicles scores 0 in protecting rear passengers' heads and necks.
According to 2012 Insurance Institute for Highway Safety (IIHS) 25% rigid barrier offset impact test results, most of vehicles cannot reach the level of excellence in the evaluation of occupant restraint because occupants' heads slide out of drivers' airbag protection range.